Electric lamp and method of operation



Aug. 29, 1933. c. G'Q FOUND ET AL. 1,924,739

ELECTRIC LAMP AND METHOD OF OPERATION I FiledJune 24,, 1930 Fig.1.

A! hart" Patented Aug. 29, 1933 UNITED STATES PATENT OFFICE ELECTRIC LAMP AND METHOD OF OPERATION York Application June 24, 1930. Serial No. 463,520 20 Claims. (QlI 176-424) Our invention relates to electric lamps in which the luminous agency is a gas or vapor. which is caused to glow by the conduction of an electric current therethrough. It is the object of our invention to provide a method of and a means for controlling, or varying at will, the light emitted by such gas conduction lamps.

Our invention is applicable to lamps from which the light is emitted mainly from the so-called positive column, that is, from an elongated luminous column located between the electrodes in which the major part of the voltage impressed on the lamp is consumed. The electrical characteristics of such positive column lamps render impracticable or uneconomic the control or variation of the light by external circuit members, such as electric resistances. The advantages of our invention are most marked in lamps having a thermionic cathode and operating with a negative characteristic, that is, requiring an increase of voltage as the current value is decreased.

In accordance with our invention the luminosity of gas conduction lamps is controlled by operating the lamps with successive discharges of short duration, conveniently with alternating current,

and timing the duration of the successive discharges to produce the desired luminous efiect.

The flow of current with respect to the anode is restrained from flowing a part of each wave of voltage in accordance with our invention by an electrostatic field to produce desired variations of light. In lamps embodying our invention a grid or control electrode surrounds the anode, or anodes respectively, and means is provided to impress on the control electrode electric charges so varying with respect to the space in the environment of the anode that a desired luminosity is obtained. In accordance with one of the features of our invention the control circuit whereby variations of light are produced is connected between the grid electrode and an electrode which serves also to maintain continuously operative an auxiliary ionizing discharge of relatively low current value.

These and other novel features of our invention will be set forth in greater particularity by the appended claims. A more complete understanding of our invention-may be obtained from the, following description taken in combination with the accompanying drawing in which Fig. 1

comprises a plan view of a lamp embodying our invention and a diagram -of electrical connections; Fig. 2 illustrates on a larger scale the anode portion of the lamp shown in Fig. 1 with part of the envelope and grid electrode shown broken away; and Figs. 3 and 4 are graphs showing the relation of the voltage and current of the main circuit to the voltage of the control circuit.

Referring to Fig. 1, the lamp here illustrated comprises an elongated envelope 1, consisting of a glass or the like (part being broken away to save space on the drawing), the envelope having outwardly extending arms 2, 3. The main portion of the envelope, which is shown broken, ordinarily is about 20 to 50 inches long. The envelope contains a suitable gas, such as neon, mercury vapor, helium, carbon dioxide, or a mixture of gases at pressures commonly employed in gas or vapor lamps, for example, at pressures of about one to five millimeters of mercury. In one end of the envelope 1 is provided a thermionic cathode made up of a hollow body or shell 4, and a heater 5, whereby the shell 4 may be maintained at a temperature of thermionic electron emissivity. The shell 4 preferably is coated with alkaline earth oxides but may be coated with a rare metal, or any other material of high electron emissivity. Various other forms of thermionic cathodes may be employed. The heater 5 is connected at one end to a leading-in conductor 6 and at the other end to the shell 4 which is in turn connected to a leading-in conductor 7. These conductors 6, 'l are connected to the secondary of a heater transformer 8 whereby electric energy is furnished to maintain the cathode at an operating temperature.

The primary of the transformer 8 is connected by the conductors 9, 10 to taps on the main transformerv 11 whereby energy is delivered both to heat the cathode and to operate the lamp as a whole as will later be described. The anodes 2, 3 consist of graphite, nickel, iron, tungsten, or other suitable conductive material. They are connected by conductors 13, 14 in series with ohmic resistances 15, 16 to the terminals of the transformer 11.

As best shown in Fig. 2, the anodes are surrounded by grids 1'7, 18, which consist either of a relatively fine mesh wire screen, or of sheet metal provided with numerous small openings, as shown in the drawing.

These grid electrodes are connected respec tively'by conductors 19, 20 to the secondary of the transformer 21, the primary of which is connected by conductors 22, 23 to the alternating current supply lines 24, 25, carrying currents of suitable frequency, say 25 or cycle current. Included in circuit with the conductor 23 is a capacitor 26 shunted by an adjustable resistor 27. By varying the resistance connected across the capacitor the phase of the alternating current furnished to the primary of the transformer 21 may be shifted at will'with respect to the 'phase of the alternating current which is supplied to the main electrodes of the lamp by the anode conductors 13, 14 and the cathode conductor 28.

Included in the cathode conductor 28 is a hand-operated switch 29 and a mercury switch 30 which is tilted by a magnet 31, the armature 32 of which is connected by suitable lever 33 to the mercury switch 30. A circuit through the mercury switch from the main transformer 11 is completed by the conductor 34 containing a resistance 35 and conductor 13.

An auxiliary electrode 36 is provided near the anode end of the lamp, this electrode being connected to the midpoint of the secondary of the transformer 21 and by the conductor 37, in circuit with a resistance 38 to the positive terminal of a direct current source (not shown) of suitable voltage. The negative terminal of the direct current source is connected by' the conductor 39 with the cathode. During operation of the device a discharge of low current value (for example, 10 to 50 milliamperes) is constantly main tained through the lamp between the cathode and the auxiliary electrode 36. The light produced by such a low current is negligible in the operation of the lamp.

When the switch 29 is closed a flow of current occurs through the circuit consisting of conductor 28, the magnet coil 31, the mercury switch 30, the conductor 34, the resistance 35 and the conductor 13. By the consequent tilting of the mercury switch, this circuit is immediately broken, thereby impressing a high potential across the lamp. If the cathode has been previously brought to an operating temperature, a positive column discharge is thereby initiated. In a lamp having a column of 4 8 inches between electrodes and a diameter of about one inch, the operating voltage is about 250 volts, most of which is consumed in the positive column. Sometimes the make and break of the starting circuit by means of the mercury switch is repeated several times before the discharge is started, this starting operation being well understood.

Were it not for the presence of the grid electrodes around the respective main anodes, the lamp would then operate with current flow during opposite half wave intervals from the cathode alternately to the respective anodes 2 and 3, the current flowing through the entire half wave interval to one of the anodes and then shifting as the polarity reverses to the other anode. Due to the presence of the negatively charged grid the flow of current does not occur to the active anode (that is, the anode which is positive at any par ticular moment) until the negative potential on the grid has fallen to a predetermined critical value. Thereupon the flow of current is initiated through the lamp to the active anode and is continued until the potential upon the anode falls below the discharge-sustaining value.

The relation of the current and voltage in the active anode circuit and the charge of the grid electrodes is illustrated by Figs. 3 and 4. In Fig. 3 the curve 40 indicates graphically the rise and fall of the alternating current voltage in the anode circuit. In Fig. 4 is shown the simultaneous variation of voltage in the circuit of the grid electrode surrounding the respective anode. At the moment the voltage in the anode circuit rises from zero, the negative voltage on the grid, as indicated by curve 41, is too high to permit the flow of current to the anode. As the positive anode voltage continues to rise, the negative grid voltage falls until a point is reached as indicated by the dotted line 42 when the grid voltage has been reduced to a critical value, at which current begins to flow from the cathode to the active anode, this current being indicated by the full line curve 43. With an increase of current through the lamp the anode voltage falls and as the current decreases again rises, as indicated by the curve44. The negative electrostatic field of the grid circuit, as indicated at 41, in the meantime falls to zero and the grid field then becomes positive. The change of grid polarity to positive produces no further effect upon thefiow of current through the lamp.

When the phase of the grid potential 41 is shifted with respect to the phase of the anode potential, then the flow of current in the anode circuit is retarded or advanced accordingly. For example, if the negative grid voltage falls to the critical starting voltage value at an earlier part of the cycle of anode voltage, then the flow of current through the lamp during the half wave interval occurs during a longer period, and conversely if the grid voltage curve is shifted to the right, then the grid potential remains above the critical voltage for a longer time and retards the flow of current to the active anode until the anode voltage has risen to a higher value than indicated graphically in Fig. 3. The interval of current flow through the lamp then is decreased. The same cycle of current fiow occurs at the opposite anode of the lamp illustrated when the polarity reverses.

Due to the persistence of vision the lamp appears to be continually luminous. It appears to be brighter or dimmer as the intervals of current shifting the phase of the grid voltages relative to the anodes through the intermediary of the phase shifting device 26, 27, and thereby timing the duration of current impulses as already explained. This operation is facilitated by the presence at all times of a small amount of ionization produced by the flow of current to the auxiliary electrode 36. Without the presence of this auxiliary electrode, a relatively long current path between the cathode and the anodes and the consequent high fall of potential would not permit a control of the discharge current in the manner described by control of the starting, of the discharge during each half wave interval. The relatively high potential drop in the positive column would either prevent or interfere with the starting of the discharges to the respective anodes.

In a copending application, Serial No. 226,275, filed October 15, 1927 by Albert W. Hull (and allowed March 23, 1933) relating to an electric lamp containing a thermionic cathode and a luminosity-producing gas such as herein shown, claims are made directed to features of construction and operation whereby the electron emissivity of the cathode and the current through the gas are so correlated that the drop of voltage at the cathode is maintained below the value at which electrical disintegration of the cathode would occur.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. The method of varying the luminosity of a positive column alternating current lamp which consists in independently impressing upon the .gated envelope,

discharge space a cyclic electric field which is capable of restraining the establishment of successive periods of current fiow and varying the phase relation of said restraining field and the voltage of said discharge in accordance with desired variations in luminosity.

2. Tne method of controlling the light emission of a positive column lamp which consists in conducting between cooperating electrodes in said gas a current falling periodically to zero and timing the duration of current impulses by an electrostatic field surrounding the positive electrode.

3. The method of controlling the luminosity of a positive column glow in a gas having a pressure of at least a millimeter of mercury which consists in conducting between cooperating elecwhich periodically are reduced the critical value at which a discharge in said gas is extinguished, and restraining the establishment of the discharge of each current wave by. a negative field adjacent the positive electrode to time the relative duration of said current waves.

4. An electric lamp .comprising an elongated envelope, a charge of luminosity-producing gas, cooperating electrodes separated a sufiicient distance in said envelope to cause the voltage drop in the positive column between said electrodes to be large relative to the combined voltage drop at said electrodes and agrid surrounding the positive electrode for timing the operation of electric discharges between said electrodes.

5'. An electric lamp comprising an elongated envelope containing a gas at a pressure of the order of several millimeters of mercury, cooperating main discharge-sustaining electrodes therein, a grid surrounding a main positive electrode, an auxiliary electrode remotefrom the cathode and means connected between said auxiliary electrode and the positive electrode which is associated with said grid for charging said grid during controlled intervals with a negative electric field of sumciently high value to restrain the operation of a positive column discharge between said main electrodes.

6. An electric lamp comprising a sealed envelope, a luminosity-producing gas therein, a cooperating anodes so located in said envelope that electric discharges may be maintained thereto through the same discharge path through said gas, an internal grid, and means for charging said grid with a variable negative potential for varying the luminosity of said lamp.

'7. A gas conduction lamp comprising an elonan attenuated gas therein, main, electrodes spaced apart a sumcient distance within said envelope to permit of the establishment of a positive column glow discharge in said gas, an auxiliary electrode, tive main electrode, and means for establishing an electric field between said grid and said auxiliary electrode.

8. A gas conduction lamp comprising a sealed envelope, an attenuated gas therein, main electrodes whereby a luminous discharge may be produced in said gas, a grid surrounding one of said electrodes, an auxiliary electrode, circuit connections between said grid and auxiliary electrode whereby an electric field may be established about said grid and means for controllably varying said field.

9. A gas conduction lamp comprising a sealed envelope, a gas therein at a pressure of about several millimeters of me cury, main electrodes a grid surrounding a posi- 3 therein spaced apart to permit of the operation of a positive column discharge in said gas, an auxiliary electrode, a source of alternating current operatively connected to said main electrodes, a source of direct current connected to said auxiliary electrode and one of said main electrodes, a gridinterposed between said main electrodes andas'ource of potential connected between said grid and said auxiliary electrode.

10. A gas conduction lamp comprising an elongated tubular envelope, a gas therein at a pressure of about several millimeters of mercury, a thermionic cathode, an anode of anodes spaced apart from said cathode a sufficient distance to permit of the operation of a positive column discharge therebetween, an auxiliary anode, a grid electrode surroundingsaid anode or anodes respectively,

an electric circuit between said grid electrode or electrodes and said auxiliary electrode and means in said circuitfor impressing a potential on said grid.

11. An electric lighting system comprising an envelope, a gas therein at a pressure of the order of a millimeter of mercury, a cathode, a main anode or anodes spaced away from said cathode in said envelope a sufiicient distance to permit of the formation of a positive column discharge, a main source of alternating current connected to said electrodes, a grid or grids for anodes, an auxiliary anode, a auxiliary anode and said grid or grids, means for shifting the phase of said grid potential with respect to said main source, and a source of direct current connected to said auxiliary a ode and said cathode.

12. An electric lighting system comprising a gas conduction lamp having a. thermionic cath-' ode, a plurality of main anodes, an auxiliary anode located nearsaid main anodes, and grid electrodes surrounding said anodes respectively, a source of alternating current connected to said cathode and said main anodes, a transformer the primary of which is also connected to said source and the secondary of which is connected to said grids and said auxiliary afnode, a phase ting device in circuit with said transformer, and means for maintaining an ionizing discharge constantly operative during the operation of said lamp from said auxiliary anode.

13. The method of operating a luminous discharge in a gas between spaced electrodes which consists in setting up in the space between saidelectrodes a restraining electrostatic field which is capable of preventing the formation of such discharge between said electrodes when the relation of said field voltages impressed on said electrodes exceed a critical value, impressing upon said electrodes voltages varying periodically from values too low to support a positive column discharge to values suflicient to start and sup-1 port such discharge and coordinating the relative value of said field and impressed variable voltage to produce a desired luminous effect.

14. The method of operating a luminous positive column discharge in a gas between a cath-' o'de and an anode spaced apart at least about 20 inches which consists in setting up in the space adjacent said anode but remote from said cathode a variable electrostatic field which is capable at a critical value of restraining the formation of such discharge between said electrodes at given impressed voltages, impressing upon said electrodes a variable current rising in voltage during each cycle to values suiliciently 150 high to start and u tain a desired discharge in said gas, and shifting the phase of said field static field between said grid and said auxiliary thermionic cathode. The method of controlling the light emis- 19. "The method of controlling the luminosity of 15. sion of an electric glow lnapositlve column lamp a lamp containing a gas and having a. main I current impulses by an independent electrostatic said lamp throughout substantially the length of eld.

16. An electric lamp comprising a sealed envelope, a luminosity-producing gas therein, 00- noslty, operating between said main electrodes too low to overcome the restraining eilect of mg th timing of said field and" the main dislation of said restraining means and the voltage cathode and an anode spaced apart so great a of said operating current to vary the light outpu distance that the major part 01 the fall of po- Said ptential in said lamp during operation is consumed A11 lamp D an elfmgated in a column of gas between said electrodes which envelope a charge lumlnoslty-plfoducmg gas, consists in producing luminosity in said lamp by F in ai envelope to cause the voltage drop periodically to a'value too low to be maintained tween said grid and said auxiliary f a region of said column of gas remote from the Operation of electric isc between said and varying the phase of said electrostatic field 18. An electric lamp comprising he Combinarents to time the duration of said intermittent tlon 01' a sealed envelope, a gas therein at a presijt t correspondjng1y varying t sure 01' several millimeters of mercury, a thermilight output onic cathode, a main anode, an auxiliary anode CLIFION G. FOUND. located adjacent said main anode, a grid within ALBERT W. HULL. said envelope, means for establishing an electror JEROME 0. SMITH. 

